1. Field of the Invention
This invention relates to a marine fender and more particularly, to an improvement of a rubbery buckling-type marine fender such as a hollow cylindrical marine fender, V-shaped marine fender, frustoconical marine fender or the like causing a buckling phenomenon in compression deformation.
2. Description of the Related Art
As an example of the conventional buckling-type marine fender, there is a rubbery hollow cylindrical marine fender of a conical trapezoidal form as shown in FIG. 1. .This marine fender comprises a main cylindrical rubber portion 2, a securing flange portion 3 for a quay wall, a shock receiving portion 4 and reinforcing steel plates 5, 6 embedded in the portions 3, 4. When such a marine fender is compressed in its axial direction by berthing of a vessel or the like thereto, there is obtained a deflection-reaction force curve absorbing a berthing energy as shown in FIG. 2. In this case, after the reaction force increases with the increase of the deflection to arrive at an upper peak (point A), it decreases to arrive at a point C though the deflection increases, and again rapidly increases with further increase of the deflection.
The marine fender exhibiting such a characteristic curve is actually used up to a point B showing the reaction force equal to the point A, in which the absorption energy of the marine fender is represented by an area surrounded by the deflection-reaction force curve and an abscissa up to the point B. However, the reaction force is actually decreased to the point C, so that the absorption energy is lost only by a portion S corresponding to an area surrounded by dotted line A-B and a curved line A-C-B. Therefore, it is required to raise the falling of reaction force represented by the point C to the dotted line A-B to increase the energy absorption by the area S.
Similarly, the above phenomenon is observed in V-shaped marine fender subjected to a berthing load in a direction perpendicular to the axial direction thereof.
In order to overcome the above problem of the conventional marine fender, there is proposed a hollow cylindrical marine fender in JP-Y-2-30505. This marine fender comprises a main cylindrical portion of a frustoconical form and a shock receiving portion of a cylindrical form, in which the loss of the absorption energy to be reduced by attempting specifying relationships between height of the main cylindrical portion and height of the shock receiving portion and between outer diameter of the shock receiving portion and inner diameter of a base of the main cylindrical portion.
According to this proposal, a timing of contacting an outer surface of the buckled main cylindrical portion with a hull of the berthing vessel is delayed by mainly making the height of the shock receiving portion relatively high, whereby the energy absorbing quantity is increased. However, since the shock receiving portion becomes higher, the deformation is necessarily caused in the shock receiving portion to create the same falling of the reaction force as in FIG. 2, so that it is not preferred to use such a marine fender in view of energy efficiency.